Video runs slow, Audio runs normal

[Veleax]

This happens a lot, buy i'm fed up. I'm playing Divx and XviD files on BSplayer. Using Win98 and have a 500Mhz comp. I play these 150+MB files, but the video is always slow, or skipping about 30 seconds of video(not good if you're reading subs). The audio runs fine, with no problems. I'm hoping I can solve this without getting a faster computer, but who knows.